This invention relates to a cloth web preshrinking apparatus of a type including an inlet roller, a heated drying drum and a shrinking blanket running onto the inlet roller and thence against an outer surface of the heated drum.
More particularly this invention relates to preshrinking, stabilizing and/or finishing knitted cloth webs. In knitted cloth, as distinguished from woven cloth, the cloth is constructed in both its lengthwise and widthwise directions by series of interlocked loops formed by continuous yarns or series of continuous yarns. As a result knitted cloth has substantial interdependence of its length and width dimensions which results in a property of being distortable easily. This distortion property has made knitted cloth desirable for many articles of apparel, because of ability of garments made from knitted cloth to conform kinesiologically to bodies and to change their shapes in response to body movements of their wearers. However this distortion property, which enhances acceptability of knitted cloth for wearing apparel, presents problems in preshrinking, stabilizing and finishing the knitted cloth webs.
Reference should be made to FIG. 6 of the drawings in regard to the following explanation. In known type of apparatus for preshrinking, stabilizing and/or finishing a knitted cloth web, as referred to before herein, a blanket 11 (usually a felt endless blanket) is led over an inlet roller 12 thereby having a first (initially outer) surface 13 of the blanket 11 stretched in a zone 14. Then the inlet roller 12 and the blanket 11 are held firmly in a nip area against an outer surface of a large diameter, rotated heated drum 15 around an arc of which the blanket 11 passes after leaving the inlet roller 12. In transferring from the inlet roller 12 to the drum 15 at the nip area, the blanket 11 reverses its curvature so that the first surface 13 of the blanket 11 contracts along its length in a compaction zone 16.
Because of the distortion property of knitted cloth, there is a tendency for the knitted cloth to lose its preshrinkage or pop out.
Electrically heated shoes 17 are provided to firmly hold the fabric 18 pressed against the working surface 13 of the blanket as the fabric is brought into engagement with the latter. Preferably the shoes press the fabric tightly against the surface 13 right into the nip area between the blanket and the drum, but due to the necessity of providing mechanical clearance between the shoes 17 and the moving surface of the drum 15, the shoes 17 used in the prior art could not maintain compression between the fabric 18 and the blanket 11 in the transition area 16 between the end of the shoes 17 and the drum 15. Because the fabric 18 is in moistened and relaxed condition before reaching the feed roller 12, it is desirable to maintain the fabric firmly against the blanket right up to the nip area between the blanket and the drum to avoid tension problems in the fabric and to prevent "pop out" of the fabric away from the blanket as it traverses the feed roller. The pop out problem is particularly troublesome with knit fabrics due to their low distortion resistance.
The cloth web 18 is fed onto the surface 13 of the blanket 11 where the surface 13 is stretched in the zone 14 due to curvature of the blanket 11 around the roller 12 and the cloth web 18 is held in contact with this surface 13, initially by means of the shoes 17 which are heated to prevent friction or sticking and then the web cloth is heated by the drum 15. As the cloth web 18 reaches a point where reversal of curvature of the blanket 11 shortens the stretched condition of the surface 13 back to normal and beyond to a contracted condition in the compaction zone 16, the cloth web 18 is compelled to shorten also because the cloth web 18 is in frictional contact with the surface 13 of the blanket 11. This shortening action is a continuous one of microscopic amounts at any instant, but which can typically total 6 inches (15.24 cm.) or more per yard (91.44 cm.) depending on thickness and material of the blanket 11 with which the apparatus is equipped.
The cloth 18 is moist before it reaches and passes under the shoes 17, so that being soft and somewhat plastic the cloth web 18 contracts readily in frictional contact with the surface 13 of the blanket. Removal of moisture by means of complete drying of the cloth web 18, by travel of the cloth web 18 over the heated drum 15, stabilizes and finishes the cloth web 18 in its contracted or preshrunk stage.
Difficulties arise in maintaining the heated shoes 17 in accurate position relative to the inlet roller 12 and with respect to the heated drum 15. The shoes 17 must generally be heated electrically and they, as well as the blanket 11, are subjected to considerable wear. The shoes 17 inevitably offer resistance to the cloth web 18 passing thereunder, which resistance increases power requirements of the apparatus. The shoes 17 are mechanically complex and expensive to repair. Adjustments of the shoes 17 and replacements of the roller 12 are necessary frequently; which adjustments and replacements make operation of the apparatus complicated, thereby increasing operator skill requirements as well as aggrevating probabilities of mistakes and presenting inherent operational errors. It is necessary to change to a larger inlet roller as the blanket wears since the position of the shoes is generally fixed.